Silanes, process for their preparation, and their use

ABSTRACT

Compounds of the formula Ia    &lt;IMAGE&gt;  (Ia)  in which X and R1 to R6 are as defined in the claims, are obtainable by reacting monochlorosilanes of the formula II    &lt;IMAGE&gt; (II)  with tetrasubstituted ethylenes of the formula III    &lt;IMAGE&gt; (III)  X as Cl and Br can be replaced by ester groups of inorganic and organic acids. The compounds of the formula I and those with other ester groups are suitable especially as a protective-group reagent for hydroxyl, mercapto, carboxyl, amino and amide groups.

This is a divisional of application Ser. No. 782,349, filed on Oct. 1, 1985, now U.S. Pat. No. 4,695,643, issued on Sept. 22, 1987.

The present invention relates to silanes having a 1,1,2,2-tetrasubstituted ethyl radical, a process for its preparation by addition of monochloromonohydrosilanes to tetrasubstituted ethylenes and to the use of the silanes as a protective-group reagent.

It is known from D. Seyferth et al., J. of Organom. Chem., 225, pages 177-191 (1982), that (1,1,2,2-tetramethylethyl)-dimethylchlorosilane is obtainable by ring opening of hexamethylsilirane with hydrogen chloride. It is also known that monochlorosilanes can be prepared by the addition of R^(a) R^(b) SiHCL to unsaturated compounds (cf. W. Noll, Chemie und Technologie der Silicone [Chemistry and Technology of the Silicones], Verlag Chemie, Weinheim, (1986), pages 45 et seq.). This reaction is catalysed by metal compounds, for example H₂ PtCl₆, it frequently being necessary to apply high pressure and/or high temperatures. Rearrangement reactions occur under these conditions, in particular if highly branched alkenes are used.

According to DE-A No. 2,804,204, it is therefore proposed to use aluminium halides of chlorine and bromine as the catalysts for this reaction. In this process, for example 2-methylbut-2-ene, a trisubstituted ethylene, is also used, (1,2-dimethylprop-1-yl)dimethylchlorosilane being obtained in high yields. This addition of, for example, dimethylchlorosilane takes place virtually only on the monosubstituted carbon atom of the trisubstituted ethylene, and not on the disubstituted carbon atom. Neither is it described in other specialist literature that the addition could take place on the disubstituted carbon atom of an ethylene.

The present invention relates to compounds of the formula I ##STR4## in which X is an ester group of an inorganic or organic acid and m is a number from 1 to 4, R¹ and R² independently of one another are linear or branched C₁ -C₁₂ -alkyl or unsubstituted or C₁ -C₆ -alkyl-substituted benzyl, C₅ -cycloalkyl or C₆ -cycloalkyl, or R¹ and R² together are tetramethylene or pentamethylene and R³ to R⁶ independently of one another are linear or branched C₁ -C₁₂ -alkyl, unsubstituted or C₁ -C₆ -alkyl-substituted phenyl or phenyl-C_(n) H_(2n) - with n=1 to 6, C₅ -cycloalkyl or C₆ -cycloalkyl, R³ and R⁵ together and/or R⁴ and R⁶ together are tetramethylene or pentamethylene, or R³ and R⁴ together and/or R⁵ and R⁶ together are trimethylene or tetramethylene, one of the radicals R¹ to R⁶ containing at least two carbon atoms it X is Cl.

An ester group X preferably is a radical of a monobasic to tetrabasic inorganic or organic acid, from which at least one acidic H atom has been removed.

The inorganic acids can be oxygen acids and oxygen-free acids. Amongst the latter, hydrochloric and hydrobromic acids (X=Cl or Br) are preferred. Examples of suitable oxygen acids are H₂ SO₄, FSO₃ H, HClO₄, H₃ PO₃ and H₃ PO₄. Other suitable oxygen acids are sulfonic acids, for example alkylsulfonic and arylsulfonic acids such as methylsulfonic acid, phenylsulfonic acid or paramethylphenylsulfonic acid or, for example, partially fluorinated or perfluorinated sulfonic acids such as fluoromethylsulfonic acid, difluoromethylsulfonic acid and trifluoromethylsulfonic acid.

Examples of suitable organic acids are aliphatic and aromatic carboxylic acids, such as formic acid, acetic acid, chloroacetic acid, trichloroacetic acid, fluoroacetic acid, trifluoroacetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, adipic acid, cyclohexanecarboxylic acid, cyclohexane-1,4-dicarboxylic acid, benzoic acid, phenylacetic acid, terephthalic acid, isophthalic acid, trimellitic acid and pyromellitic acid.

Particularly preferably X is -Cl, -Br, CH₃ SO₃ - or CF₃ SO₃ - and especially Cl.

In formula I, m preferably is one of the numbers 1 to 3, in particular 1 or 2 and especially the number 1.

In a preferred embodiment, R¹ and R² are identical radicals. Preferably, R¹ and R² are C₁ -C₆ -alkyl, especially C₁ -C₄ -alkyl.

Examples of alkyls R¹ and R² as well as R³ and R⁶ are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tertiary-butyl, pentyl, hexyl, heptyl, octyl, decyl and dodecyl. Particularly preferably, R¹ and R² are methyl.

Examples of substituted benzyls R¹ and R² are trimethylbenzyl, propylbenzyl, butylbenzyl, methylbenzyl, ethylbenzyl and dimethylbenzyl.

Examples of cycloalkyls R¹ and R² are cyclopentyl, methylcyclopentyl, cyclohexyl and methylcyclohexyl.

Alkyls R³ to R⁶ preferably contain 1 to 6 carbon atoms, especially 1 to 4 carbon atoms. Examples of R¹ and R² have been mentioned. The preferred alkyl radicals are methyl, ethyl, propyl and butyl.

Substituted phenyls R³ to R⁶ can, for example, be methylphenyl, dimethylphenyl or ethylphenyl. In the formula phenyl-C_(n) H_(2n) -, n is preferably 1 or 2. Examples are benzyl, methylbenzyl, ethylbenzyl, phenylethyl and methylphenylethyl.

In a preferred embodiment, R³ to R⁶ in the formula I are independently of one another C₁ -C₆ -alkyl, cyclopentyl or cyclohexyl, or R³ and R⁵ and/or R⁴ and R⁶ are pentamethylene or R³ and R⁴ and/or R⁵ and R⁶ are tetramethylene.

In another preferred embodiment, alkyls R³ to R⁶ independently of one another are methyl, ethyl, propyl, i-propyl, n-butyl, i-butyl or t-butyl.

In a further preferred embodiment, X is Cl and R¹ and R² are methyl, and one of the radicals R³ to R⁶ is ethyl and the others are methyl, or R³ and R⁴ are ethyl and R⁵ and R⁶ are methyl, or R³ to R⁶ are ethyl.

It has been found, surprisingly, that compounds of the formula Ia, in which X is Cl or Br, are obtained in high yields and purities when the addition of disubstituted chlorosilanes to tetrasubstituted ethylenes is catalysed by aluminium halides. In spite of the high degree of branching, virtually no isomerisations of the tetrasubstituted ethylenes are observed.

The invention also relates to the process for the preparation of compounds of the formula Ia ##STR5## in which X¹ is Cl or Br, R¹ and R² independently of one another are linear or branched C₁ -C₁₂ -alkyl, C₅ -cycloalkyl or C₆ -cycloalkyl or unsubstituted or C₁ -C₆ -alkylsubstituted benzyl, or R¹ and R² together are tetramethylene or pentamethylene, and R³ to R⁶ independently of one another are linear or branched C₁ -C₁₂ -alkyl, unsubstituted or C₁ -C₆ -alkyl-substituted phenyl or phenyl-C_(n) H_(2n) - with n=1 to 6, C₅ -cycloalkyl or C₆ -cycloalkyl, R³ and R⁵ together and/or R⁴ and R⁶ together are tetramethylene or pentamethylene, or R³ and R⁴ together and/or R⁵ and R⁶ together are trimethylene or tetramethylene, by addition of a monohalogenosilane of the formula II ##STR6## in which R¹, R² and X are as defined above, to a substituted ethylene in the presence of catalytic amounts of aluminium trichloride, aluminium tribromide, alkylaluminium dichloride, alkylaluminium dibromide, aluminium oxide-chloride, aluminium oxide-bromide or mixtures thereof at temperatures of at most 60° C., wherein the ethylene is a tetrasubstituted ethylene of the formula III ##STR7## in which R³ to R⁶ are as defined above.

The preferred meanings given above apply to R¹ to R⁶, and additionally R¹ to R⁶ can also be methyl.

The alkyl group in an alkylaluminium dichloride or dibromide preferably contains 1 to 12, in particular 1 to 6 and especially 1 to 4 carbon atoms. Examples are methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, hexyl, octyl, decyl and dodecyl.

The catalyst used is preferably AlCl₃ and/or C₁ -C₄ -alkyl-AlCl₂. The reaction temperature preferably is 0° to 60° C., in particular 20° to 40° C. The reaction is exothermic and cooling is necessary in general in order to maintain the reaction temperature. The catalyst can be used in amounts of 0.01 to 20% by weight, in particular 0.1 to 10% by weight and especially 0.1 to 5% by weight, relative to the reactants.

The reaction is preferably carried out under a blanketing gas atmosphere, for example nitrogen, helium or argon. Application of a positive pressure is advantageous when gaseous reactants are employed. Since the reactants are liquids in most cases, the use of inert solvents is superfluous. To avoid the formation of hydrolysed by-products, exclusion of moisture must be ensured.

The reaction products are worked up by conventional methods, the catalyst being generally separated off first, for example by addition of the solvent (hydrocarbons) for the reaction product and filtration. The solvent can then be removed and the crude product can be purified by known processes, for example by distillation and/or chromatographic methods. In many cases, the desired silane can be isolated by direct distillation of the reaction mixture.

Compounds of the formula I, in which X is the ester group of an oxygen acid, can be prepared by reacting compounds of the formula Ia with oxygen acids, with elimination of HBr or HCl, in a manner known per se. The reaction can be carried out in an inert solvent and, if appropriate, with the addition of bases such as tertiary amines, in order to fix the HCl or HBr formed.

Examples of suitable inert solvents are substituted or unsubstituted hydrocarbons, ethers and esters.

The compounds of the formula I including (1,1,2,2-tetramethyl-eth-1-yl)-dimethylchlorosilane are outstandingly suitable as a protective-group reagent. Compared with known silylation reagents, for example tertiary-butyldimethylchlorosilane [cf. Synthetic Communications, 9(4), 295-299 (1979)] or (1,1,2-trimethyleth-2-yl)-dimethylchlorosilane (cf. DE-A No. 2,804,204), they have a substantially improved hydrolytic stability. In addition, the compounds have a more pronounced lypophilic character which can be influenced by the number of carbon atoms in the R³ to R⁶ groups and thus adapted to specific reaction conditions. Due to the improved hydrolytic stability, the reaction medium can be varied more widely.

The invention also relates to the use of compounds of the formula Ib ##STR8## in which X is an ester group of an inorganic or organic acid and m is an integer from 1 to 4, R¹ and R² independently of one another are linear or branched C₁ -C₁₂ -alkyl, C₅ -cycloalkyl or C₆ -cycloalkyl or unsubstituted or C₁ -C₆ -alkyl-substituted benzyl, or R¹ and R² together are tetramethylene or pentamethylene and R³ to R⁶ independently of one another are linear or branched C₁ -C₁₂ -alkyl, unsubstituted or C₁ -C₆ -alkyl-substituted phenyl or phenyl-C_(n) H_(2n) - with n=1 to 6, C₅ -cycloalkyl or C₆ -cycloalkyl, R³ and R⁵ together and/or R⁴ and R⁶ together are tetramethylene or pentamethylene or R³ and R⁴ together and/or R⁵ and R⁶ together are trimethylene or tetramethylene, as a removable protective-group reagent for hydroxyl, mercapto, carboxyl, amino and amide groups.

The present invention also relates to a process for protecting hydroxyl, mercapto, carboxyl, amino and amide groups in organic syntheses, which comprises reacting an organic compound carrying hydroxyl, mercapto, carboxyl groups or alkali metal salts thereof, amino and/or amide groups, or an aldehyde or ketone having an α-H atom, with a compound of the formula I ##STR9## and, after the synthesis reaction has been carried out, eliminating the protective group in a manner known per se.

The preferred meanings given above apply to R¹ to R⁶, and R¹ to R⁶ preferably can also be methyl. Exampels of suitable alkali metal salts of alcohols, thiols and carboxylic acids are the lithium salts and in particular the sodium salts.

The amino or amide groups can be partially substituted by aliphatic or aromatic groups. The amide group can also be present in the form of a lactam.

Suitable aldehydes and ketones are of the formulae IV and V ##STR10##

In the reaction with a protective-group reagent of the formula Ib, vinyl silyl ethers of the formulae Iva and Va ##STR11## are then formed.

R⁷, R⁸, R¹⁰ and R¹¹ are hydrogen atoms or organic radicals which contain preferably 1 to 30, in particular 1 to 20 and especially 1 to 16 carbon atoms. R⁹ is such an organic radical. R¹² is the radical ##STR12##

Examples of organic radicals R⁷, R⁸, R⁹, R¹⁰ and R¹¹ are aliphatic, cycloaliphatic, heterocyclic, aromatic or heteroaromatic radicals. The radicals can be unsubstituted or substituted by, for example, C₁ -C₁₂ -alkyl, C₁ -C₁₂ -alkoxy, C₁ -C₁₂ -alkylthio, halogen, such as F, Cl and Br, phenyl or benzyl.

The aliphatic radical can be linear or branched alkyl, in particular alkyl having 1 to 12 carbon atoms. The cycloaliphatic radical can contain 3 to 12, in particular 3 to 7 ring carbon atoms. The heterocyclic radical can contain 1 to 3 hetero-atoms and 3 to 7 ring members in total. The heteroaromatic radical preferably contains 1 or 2 hetero-atoms and preferably 5 or 6 ring members in total. The aromatic radical is preferably phenyl, naphthyl, anthranyl or phenanthryl.

R⁷ and R⁸ as well as R⁹ and R¹⁰ can, together with the carbon atoms to which they are linked, also form a cycloaliphatic or heterocyclic radical having 3 to 7 ring members in total and preferably 1 or 2 hetero-atoms. The heterocyclic radicals are not bonded via hetero-atoms to the CH groups or CO groups in the formulae IV and V.

The protective group is introduced in the conventional manner under mild conditions, in most cases at room temperature up to temperatures of about 100° C., by reacting a compound of the formula I with a compound which contains the group to be protected (latent), if appropriate in the presence of an organic base as an acceptor for acids formed. Preferred suitable organic bases are tertiary amines, for example trimethylamine, triethylamine, tributylamine, N-methylpiperidine, N-methylpyrrolidine, pyridine or imidazole. The reaction is in general carried out in the presence of inert solvents. Polar solvents such as ethers, N-substituted lactams or N-disubstituted acid amides, for example dioxane, dibutyl ether, tetrahydrofuran, dimethylformamide, dimethylacetamide, hexamethylphosphoric acid triamide and N-methylpyrrolidone are particularly suitable.

The protected compound is isloated by conventional methods, for example by distillation, crystallisation or chromatography.

The preparation of compounds with a protective group according to the invention from compounds of low reactivity, for example tertiary alcohols, is advantageously carried out in such a way that corresponding silyl esters of strong acids, for example trifluoromethanesulfonic acid, are reacted in the presence of a base with a compound containing the group which is to be protected.

The silyl-protective group is eliminated in accordance with conventional methods by the action of aqueous acids, or bases, optionally in the presence of inert solvents, by the action of Lewis acids, of quaternary ammonium fluorides or the action of HF/urea mixtures. The silanol formed in the hydrolysis can be converted in a simple manner, for example with SOCl₂ or PCl₃ or PCl₅, into the chlorosilane of the formula Ia.

The examples which follow explain the invention in more detail.

(A) PREPARATION OF MONOCHLOROSILANES Example 1: Preparation of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane

100 ml (0.92 mol) of dimethylchlorosilane and 3.8 g (0.028 mol) or aluminium chloride are introduced into a 500 ml three-necked flask with a reflux condenser and dropping funnel. Within 1 hour, 109.5 ml (0.92 mol) of tetramethylethylene are added dropwise. The reaction temperature is maintained in the range from 25° to 30° C. by external cooling. After 4 hours, undissolved aluminium chloride is filtered off from the reaction solution which is then distilled.

This gives 141 g of product (86% yield), boiling point: 62°-64° C./20.8 mbar. The ¹ H-NMR spectrum is in agreement with the structure.

Example 2: Preparation of (1,1,2,2-tetraethyl-eth-1-yl)-dimethylchlorosilane

2.1 g of tetraethylethylene, 2 ml (18 mmol) of dimethylchlorosilane and 200 mg of AlCl₃ are reacted according to Example 1. After 2 hours, the reaction mixture is diluted with pentane and the precipitate is filtered off. The pentane is stripped from the filtrate in vacuo and the residue is distilled. This gives 2.8 g (80% of theory) of product as a colourless liquid. Boiling point=75°-80° C./0.195 mbar.

Analysis: calculated: C 61.36 H 11.59 Cl 15.09 Si 11.96; (C₁₂ H₂₇ ClSi) found: C 61.69 H 11.49 Cl 14.88 Si 12.08.

Example 3: Preparation of (1,2-diethyl-1,2-dimethyleth-1-yl)dimethylchlorosilane

According to Example 2, 200 mg of 3,4-dimethylhex-3-ene, 0.2 ml (1.8 mmol) of dimethylchlorosilane and 50 mg (0.37 mmol) of AlCl₃ are reacted and the product is worked up. This gives 180 mg (50% of theory) of colourless liquid of boiling point=95°-97° C./0.26 mbar.

Example 4: Preparation of ##STR13##

According to Example 2, 1.1 g of ##STR14## 1 ml (9 mmol) of dimethylchlorosilane and 150 mg of AlCl₃ are reacted and the product is worked up. This gives 1.2 g (67% of theory) of a colourless oil of boiling point =100°-105° C./0.065 mbar.

Example 5: Preparation of ##STR15##

12.0 g (0.088 mol) of methyl-butyl-chlorosilane, prepared from methyl-dichlorosilane and n-butyl-lithium, and 1.17 g (8.8 mmol) of aluminium chloride are introduced into a 100 ml three-necked flask with reflux condenser and dropping funnel. Within 15 minutes, 7.4 g (0.088 mol) of tetramethylethylene are added dropwise. The reaction temperature is maintained in the range from 20° to 25° C. by external cooling. After one hour, the product is isolated by distillation.

This gives 15.6 g of product, boiling point: 98°-100° C./20.8 mbar (80% of theory). The ¹ H-NMR spectrum is in agreement with the structure.

Example 6: Ethyl-aluminium dichloride as the catalyst

1.03 ml (10 mmol) of ethyl-aluminium dichloride are introduced in 21.6 ml (0.2 mol) of dimethylchlorosilane into a 100 ml three-necked flask with reflux condenser and dropping funnel. Within 30 minutes, 23.9 ml (0.2 mol) of tetramethylethylene are added dropwise. The reaction temperature is maintained in the range from 20° to 25° C. by external cooling. After one hour, the reaction solution is distilled.

This gives 22.1 g of product (62% of theory), boiling point: 62°-64° C./20.8 mbar.

Example 7: Isopropyl-aluminium dichloride as the catalyst

1.37 ml (10 mmol) of isopropyl-aluminium dichloride are introduced into 21.6 ml (0.2 mol) of dimethylchlorosilane into a 100 ml three-necked flask with reflux condenser and dropping funnel. Within 30 minutes 23.9 ml (0.2 mol) of tetramethylethylene are added dropwise. The reaction temperature is maintained in the range from 20° to 25° C. by external cooling. After one hour, the reaction solution is distilled.

This gives 25.9 g of product (72% of theory), boiling point: 62°-64° C./20.8 mbar.

(B) APPLICATION EXAMPLES Example 8: ##STR16##

1 g (3.86 mmol) of the silyl chloride are added to a mixture of 0.31 g (4.5 mmol) of imidazole and 0.46 g (4.3 mmol) of benzyl alcohol in 5 ml of DMF. After stirring at room temperature for 16 hours, working-up is carried out as follows: the reaction mixture is diluted with hexane and washed several times with water. The organic phase is then dried with MgSO₄ and evaporated. After chromatography on silica gel, 1.77 g of the desired silyl ether (92% of theory) are isolated as a colourless oil.

Analysis: calculated: C 76.30 H 10.37 Si 8.50; (C₂₁ H₃₄ OSi) found: C 76.32 H 10.36 Si 8.71.

Example 9: Preparation of: ##STR17##

2.0 g (8.5 mmol) of (1,1,2,2-tetraethyleth-1-yl)-dimethylchlorosilane are, as described in Example 8, stirred with 519 mg (7 mmol) of n-butanol in the presence of 578 mg (8.5 mmol) of imidazole in 5 ml of DMF for 16 hours at room temperature. The mixture is worked up as described in Example 8.

After chromatography on silica gel and subsequent distillation, 1.71 g (90% of theory) of a colourless oil of boiling point=80°-85° C./0.0665 mbar are isolated.

Analysis: C₁₆ H₃₆ OSi) calculated: C 70.51 H 13.31 Si 10.31; found: C 70.25 H 13.19 Si 10.3.

Example 10: Preparation of ##STR18##

The reaction is carried out in accordance with Example 9, wtih cyclohexanol in place of n-butanol. This gives a colourless oil of boiling point=100°-105° C./0.039 mbar.

Analysis: (C₁₈ H₃₈ OSi) calculated: C 72.41 H 12.83 Si 9.41; found: C 72.20 H 12.99 Si 9.81.

Example 11: Preparation of ##STR19##

Analogously to Example 8, 1.08 g (10 mmol) of benzyl alcohol are reacted in the presence of 1.02 g (15 mmol) of imidazole in 10 ml of DMF with 1.95 g (11 mmol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane for 16 hours at room temperature. After distillation of the crude product, 2.15 g (86% of theory) of a colourless oil of boiling point=105°-110° C./0.026 mbar are obtained.

Analysis: (C₁₅ H₂₆ OSi) calculated: C 71.93 H 10.46 Si 11.21; found: C 71.80 H 10.38 Si 11.34.

Example 12: Preparation of ##STR20##

Analogously to Example 8, 1.0 g (10 mmol) of cyclohexanol are reacted in the presence of 1.02 g (15 mmol) of imidazole in 10 ml of DMF with 1.96 g (11 mmol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane for 16 hours at room temperature. The mixture is worked up as described and, after distillation of the crude product, 2.25 g (93% of theory) of colourless oil of boiling point=49°-51° C./0.026 mbar are obtained.

Analysis: (C₁₄ H₃₀ SiO) calculated: C 69.35 H 12.47 Si 11.58; found: C 69.37 H 12.23 Si 12.01.

Example 13: Preparation of ##STR21##

The reaction is carried out in accordance with Example 8, using 5.19 g (70 mmol) of n-butanol, 7.15 g (0.105 mmol) of imidazole. 13.74 g of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane in 50 ml of dimethylformamide (DMF).

Yield: 13.17 g (87% of theory); boiling point=104°-106° C./26 mbar.

Analysis: (C₁₂ H₃₈ SiO) calculated: C 66.59 H 13.04 Si 12.98; found: C 66.41 H 13.13 Si 13.34.

Example 14: Preparation of: ##STR22##

(a) Preparation of (1,1,2,2-tetramethyleth-1-yl)-dimethylsilyl trifluoromethanesulfonate

50 ml of trifluoromethanesulfonic acid are slowly added dropwise at room temperature under argon to 101.57 g (0.57 mol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane. Subsequently, the mixture is heated for 8 hours at 60° C. After this time, the evolution of HCl ceases. 111 g (67% of theory) of a colourless oil of boiling point=123°-124° C./28.6 mbar are obtained by distillation. The ¹ H-NMR spectrum is in agreement with the structure.

(b) Reaction of the silyl ester according to (a) with 2-methylbutan-2-ol.

A mixture of 9.75 g (0.091 mol) of 2,6-lutidine and 6.17 g (0.07 mol) of 2-methyl-2-butanol is added dropwise at 0° C. under argon to 22.44 g (0.07 mol) of the silyl ester in 100 ml of methylene chloride. After stirring at room temperature for 4 hours, the mixture is poured on ice and extracted with hexane.

The combined hexane phases are washed with water, dried with MgSO₄ and concentrated in vacuo. From 15.65 g of crude product, 13.5 g of a colourless oil (84% of theory) of boiling point 118°-120° C./30 mbar are isolated by distillaton.

Analysis: (C₁₃ H₃₀ SiO) calculated: C 67.75 H 13.12 Si 12.19; found: C 68.01 H 12.96 Si 12.52.

Example 15: Preparation of ##STR23##

20.44 g (0.07 mol) of the silyl ester according to Example 14a are introduced into 80 ml of methylene chloride. A mixture of 9.75 g (0.091 mol) of 2,6-lutidine and 10.5 g (0.07 mol) of 2-methyl-1-phenyl-2-propanol is added dropwise at 5° C. under argon. The mixture is then stirred for 8 hours at room temperature. The mixture is poured on ice and extracted with hexane. The combined hexane phases are washed with water and then dried with MgSO₄. The hexane is removed in vacuo and the residue is subjected to chromatography on silica gel. This gives 16.79 g of a colourless liquid (82% of theory). Boiling point=84°-85° C./0.026 mbar.

Analysis: (C₁₈ H₃₂ OSi) calculated: C 73.90 H 11.03 Si 9.60; found: C 73.79 H 11.21 Si 9.80.

Example 16: Preparation of ##STR24##

5.0 g (0.037 mol) of phenylacetic acid are added in portions to a solution of 7.8 g (0.044 mol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane and 4.8 g (0.047 mol) of triethylamine in 50 ml of dimethylformamide. The mixture is stirred for 2 hours at room temperature and then taken up in hexane and washed with water. The hexane phase is dried with Na₂ SO₄ and the evaporation residue is subjected to chromatography on silica gel with hexane/ethyl acetate and then distilled. This gives 6.11 g (59% of theory), boiling point=134°-136° C./2 mbar. The ¹ H-NMR spectrum is in agreement with the structure.

Example 17: Preparation of ##STR25##

9.1 g (0.09 mol) of butylmercaptan in 50 ml of hexane are slowly added dropwise to 2.3 g (0.1 mol) of sodium in 50 ml of hexane under argon. The mixture is stirred overnight at room temperature and then heated under reflux for 1 hour. 16.0 g (0.09 mol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane in 25 ml of hexane are then slowly added dropwise, while cooling in an ice bath. After heating under reflux for 2 hours, the mixture is concentrated in vacuo and the residue is distilled. This give 13.2 g of an oil of boiling point 128°-130° C./2.6 mbar. The ¹ H-NMR spectrum is in agreement with the structure.

Example 18: Preparation of ##STR26##

17.85 g (0.1 mol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane are introduced under an inert gas into a 50 ml three-necked flask with dropping funnel and reflux condenser. 8.79 ml (0.1 mol) of trifluoromethanesulfonic acid are added dropwise at room temperature within 10 minutes. The mixture is then heated for 4 hours at 60° C. After the evolution of HCl gas has ceased, the mixture is cooled and then distilled.

23.4 g of the desired silyl ester (80% of theory) are isolated as a colourless liquid, boiling point 39°-42° C./0.026 mbar.

Example 19: Preparation of ##STR27##

2.0 g (20 mmol) of pinacolin and 2.22 g (22 mmol) of triethylamine are cooled in 20 ml of ether under an inert gas to 0° C. 4.88 g (17 mmol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylsilyl-trifluoromethanesulfonate are added dropwise with stirring at 0°-5° C. Stirring is then continued for a further 4 hours at room temperature. The ether phase is separated off and distilled in a bulb tube oven. This gives 3.5 g of a colourless oil (87% of theory), boiling point 105°-110° C./20.8 mbar. ¹ H-NMR (CDCl₃, 250 MHz): δ: 0.22(s. 6H, Si(CH₃)), 0.94 (d, J=6 Hz, 6H, (CH₃)₂ CH); 0.96 (s, 6H, (CH₂)₂ C); 1.06 (s, 9H) C(CH₃)₃); 1.70 (m, 1H, HC(CH₃)₂), 5.89 (d, J=0.5 Hz, 1H=CH), 4.03 (d, J=0.5 Hz, 1H).

Example 20: Preparation of ##STR28##

1.16 g (20 mmol) of propionaldehyde and 2.22 g (22 mmol) of triethylamine are cooled in 20 ml of ether under an inert gas to 0° C. 4.88 g (17 mmol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylsilyl-trifluoromethanesulfonate are added dropwise with stirring at 0°-5° C. Stirring is then continued at room temperature for a further 4 hours. The ether phase is separated off and distilled in a bulb tube oven. This gives 2.45 g of a colourless oil (73% of theory), boiling point 125°-130° C./20.8 mbar.

¹ H-NMR (CDCl₃, 250 MH₂): δ: 0.16 (s, 6H, Si(CH₃)₂); 0.90 (s, 6H, (CH₃)₂ C); 0.94 (d, J=6 Hz, 6H, (CH₃)₂ CH); 1.57 (dd, J=6 Hz, 0,5 Hz, 3H, CH₃ CH); 1.65 (m, 1H, CH(CH₃)₂); 4.60 (m, 1H=CH-CH₃); 6.17 (m, 1H, CH-O).

Example 21: Preparation of ##STR29##

6.4 g (29 mmol) of methyl-butyl-(1,1,2,2-tetramethyleth-1-yl)-chlorosilane are added to a mixture of 2.49 g (36.5 mmol) of imidazole and 2.95 g (24 mmol) of 1-phenyl-ethanol in 30 ml of DMF. After stirring at room temperature for 16 hours, the mixture is worked up as described in Example 8. After distillation in a bulb tube oven, 6.54 g of the desired silyl ether (88% of theory) are isolated as a colourless oil. Boiling point: 115°-120° C./0.26 bar.

Example 22: Preparation of ##STR30##

17.9 g (0.1 mol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylsilyl chloride, 6.8 g (0.1 mol) of imidazole and 60 ml of triethylamine are added together and stirred for 40 hours at room temperature. The mixture is then diluted with 100 ml of hexane, filtered and concentrated. Distillation of the residue thus obtained gives 17.3 g (82% of theory) of a product of boiling point 79°-81° C./0.065 mbar.

Example 23: Preparation of ##STR31##

46.1 g (0.26 mol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylsilyl chloride, 28.1 g (0.28 mol) of triethylamine and 17 g (0.2 mol) of pyrrolidone are stirred at room temperature for 3.5 hours in 100 ml of dimethylformamide. The mixture is then diluted with 200 ml of hexane and washed with ice cold water and 1-molar aqueous oxalic acid. Drying of the hexane phase with sodium sulfate and concentrating gives, after distillation, 40.6 g (90% of theory) of product, boiling point 78°-82° C./0.026 mbar.

Example 24: Preparation of ##STR32##

80.7 g (0.8 mol) of triethylamine are added to 20 g (0.27 mol) of 1-amino-2-methoxyethane and 57 g (0.32 mol) of (1,1,2,2-tetramethyleth-1-yl)-dimethylsilyl chloride in 100 ml of hexane and the mixture is stirred at room temperature for 3.5 hours. The mixture is then diluted with 100 ml of hexane and filtered, and the evaporation residue is distilled: 37.7 g (58% of theory) of product of boiling point 54°-58° C./0.065 mbar.

Example 25: Preparation of ##STR33##

127.0 g of (1,1,2,2-tetramethyleth-1-yl)-dimethylchlorosilane (0.71 mol) are dissolved in 500 ml of dimethylformamide and 72.4 g of triethylamine (0.72 mole) are added. 132.3 g of benzyl (4S)-azetidine-2-one-4-carboxylate (0.645 mol) are then introduced in portions while cooling in a waterbath such that the internal temperature is 25°-30° C. The resulting white, thick suspension is then stirred for 2 hours at room temperature. The mixture is taken up in 1000 ml of hexane and washed successively with 1000 ml of water, 80 ml of 1-molar oxalic acid and 2×1000 ml of water. After drying with sodium sulfate and distilling off the hexane, a slightly yellowish evaporation residue is obtained.

Yield: 225.7 g, corresponding to 99% of theory. A thin-layer chromatogram (silica gel, 2:l hexane/ethyl acetate as solvent) shows a single product. R_(f) value: 0.58.

Example 26:

The silyl ethers listed in the table which follows are cleaved at room temperature under the reaction conditions indicated. The results are shown in the table.

    __________________________________________________________________________      Reaction conditions                                                                          ##STR34##                                                                                    ##STR35##                                                                                        ##STR36##                       __________________________________________________________________________     1% HCl/ethanol (EtOH)                                                                        complete cleavage after                                                                      complete cleavage after                                                                          no cleavage after 6 hours,                     30 minutes    137 minutes       16% cleavage after 72                                                          hours                            n-Bu.sub.4 NF/tetrahydrofuran                                                                complete cleavage after                                                                      complete cleavage after                                                                          no cleavage                      (THF)         <3 hours      about 24 hours                                     THF:acetic acid:H.sub.2 O = 1:3:1                                                            complete cleavage after                                                                      20% cleavage after 24 hours                                                                      no cleavage                                    24 hours      50% cleavage after 48 hours                        NaOH (5%)/EtOH                                                                               no cleavage after 24 hours                                                                   stable over 24 hours                                                                             no cleavage                      n-Butyl.sub.4 NF on silica gel                                                               complete cleavage after                                                                      30% cleavage after 6 hours                                                                       no cleavage                                    <4 hours      85% cleavage after 72 hours                        5 equivalents of HF/                                                                         complete cleavage after                                                                      cleavage complete after                                                                          50% cleavage after 22                                                          hours                            urea cyclohexane                                                                             about 25 minutes                                                                             30 minutes        67% cleavage after 40                                                          hours                            BF.sub.3 (gas)/cyclohexane                                                                   complete cleavage after                                                                      cleavage complete after                                                                          cleavage complete after                        about 40 minutes                                                                             40 minutes        20 minutes                                                                      ##STR37##                       __________________________________________________________________________

Example 27: Cleavage of ##STR38## with HCl(1%)/ethanol: cleavage complete after 24 hours. With NaOH(5%)/ethanol: cleavage complete after 3 hours. Example 28: Cleavage of ##STR39## with HCl(1%)/ethanol: cleavage complete after <5 minutes With NaOH(5%)/ethanol: cleavage complete after <2 hours 

What is claimed is:
 1. A process for protecting hydroxyl, mercapto, carboxyl, amino and amide groups in organic syntheses, which comprises reacting an organic compound carrying hydroxyl, mercapto, carboxyl groups or alkali metal salts thereof, amino and/or amide groups, or an aldehyde or a ketone having an α-H atom with a compound of the formula Ib ##STR40## in which X is an ester group of an inorganic or organic acid and m is a number from 1 to 4, R¹ and R² independently of one another are linear or branched C₁ -C₁₂ -alkyl, C₅ -cycloalkyl or C₆ -cycloalkyl or unsubstituted or C₁ -C₆ -alkyl-substituted benzyl, or R¹ and R² together are tetramethylene or pentamethylene and R³ to R⁶ independently of one another are linear or branched C₁ -C₁₂ -alkyl, unsubstituted or C₁ -C₆ -alkyl-substituted phenyl or phenyl-C_(n) H_(2n) - with n=1 to 6, C₅ -cycloalkyl or C₆ -cycloalkyl, R³ and R⁵ together and/or R⁴ and R⁶ together are tetramethylene or pentamethylene or R³ and R⁴ together and/or R⁵ and R⁶ together are trimethylene or tetramethylene, to form a removable protective group on said organic compound, and eliminating the protective group after the organic synthesis reaction has been carried out. 